This invention relates to photoelectric sensors and more particularly to photoelectric reflective sensors used as proximity sensors, i.e. for detecting the presence of an object in a sensing region. Sensors of this type are referred to as diffuse reflective sensors inasmuch as they do not require a specially reflective surface to reflect a beam of light, but reflect diffuse light off an ordinary surface of an object to be detected.
Diffuse reflective photoelectric sensors have a light emitting element directing a beam of light out to or toward a sensing region. They also have a light detecting element such as a phototransistor or a photodiode similarly directed toward the sensing region. Lenses may be used to focus the beam of light. The light detecting element operates to provide an electric output signal when light of a predetermined intensity is received by that element. This occurs when a target object is present at a predetermined distance from the sensor whereby the beam of light from the emitting element is reflected from the target object back to the detecting element with sufficient intensity to operate the detecting element. It is necessary to provide adjustment of the sensing distance in order for such sensors to be practicably usable in industrial environments. Such adjustment may be accomplished mechanically wherein the light emitting element and the light detecting element are aimed along intersecting lines and one or both of such elements are mechanically pivotably adjustable to increase or decrease the angle of intersection, thereby shortening or lengthening the distance of the target sensing region, respectively. Another means of increasing or decreasing the target distance from the sensor is to adjust the electronics such as by adjusting a gain potentiometer while monitoring the output when the sensor is aimed at the target at the desired distance. This adjustment is difficult to make when the sensor incorporates a timed output. Moreover, access to such potentiometers usually requires a hole through the housing, which hole needs to be covered or plugged after the adjustment for applications of the sensor.